The present invention relates to a headlight system for vehicles, and more particularly, to a daytime running light (DRL) system in which intensity of DRLs may be controlled.
A headlight system for vehicles is generally used during nighttime driving or when the ambient light is low, to provide illumination of the road and of other vehicles to the driver, and also to enable drivers of other vehicles to view the vehicle. The headlight system is normally activated at dusk. It is also frequently used in bad weather such as when it is raining or snowing, again both for better illumination of the road and other vehicles, and to allow the drivers of other vehicles to view the vehicle.
For many countries located in far northern latitudes such as the Scandinavian countries and Canada, DRL laws have been enacted in an effort to reduce the number of accidents. That is, the DRL laws make necessary the illumination of the headlights during daytime hours (in the case of Canada, only vehicles manufactured since 1989 must comply with this law). The DRLs operate such that the headlights are automatically turned on at a predetermined brightness during the day.
In the case of the Scandinavian countries, the low beams are used as the DRLs, but in Canada the high beams are used since the headlights will last far less time if the low beams are used both during the day and at night. However, with the use of high beams, glare becomes a significant problem to drivers in oncoming traffic and to vehicles in front of the vehicle using the DRLs. Accordingly, a method has been employed in which 1.6 to 2.0 ohm(xcexa9) resistors are used to reduce the amount of current supplied to the headlights, thereby lowering the intensity of the high beams.
However, during operation to reduce the intensity of the high beams, heat is generated by the resistors. This may damage elements in close proximity to the resistors. Also, the generation of heat by the resistors makes resistor layout design in the compactly formed DRL system difficult.
In a preferred embodiment of the present invention current applied to headlights in a daytime running light (DRL) system (headlights as referred to herein are to be understood as being high beam headlights) is controlled to limit the intensity of the headlights using a current loop structure that utilizes a transistor array.
In one embodiment, the present invention provides a control system for daytime running lights including a controller for controlling DRLs according to whether the ignition is ON and information received from a combination switch, and a plurality of switches that are switched according to signals from the controller. Preferably the switches comprise four transistors. The first transistor has a collector terminal connected to the battery, an emitter terminal connected to a first of two terminals of a left headlight, and a base terminal connected to the controller. The second transistor has a collector terminal connected to a second terminal of the left headlight, an emitter terminal grounded, and a base terminal connected to the controller. The third transistor has a collector terminal connected to the second terminal of the left headlight, an emitter terminal connected to a first of two terminals of a right headlight (a second terminal of the right headlight being grounded), and a base terminal connected to the controller. The fourth transistor has a collector terminal connected to the battery, an emitter terminal connected to the first terminal of the right headlight, and a base terminal connected to the controller.
The controller, if it determines that DRL operational conditions are satisfied, forms a closed loop with the battery, the first transistor, the left headlight, the third transistor, the right headlight, and ground (preferably in this sequence) such that a current available to each headlight from the battery is reduced by one half as a result of the internal resistance of the right headlight and the left headlight. However, the controller, if it determines that conditions for operating high beams are satisfied, forms an independent loop with the battery, the first transistor, the left headlight, the second transistor, and ground (again, preferably in this sequence); and another independent loop with the battery, the fourth transistor, the right headlight, and ground (in this sequence), thereby supplying a current that is not reduced to the left and right headlights.
In another aspect of the present invention, a control system for daytime running lights includes a controller and a switch unit. The controller receives ON/OFF signals from the ignition switch and combination switch ON/OFF signals, and controls illumination intensity of left and right headlights according to the received signals. The switch unit is connected to the battery, the left and right headlights, and the controller. The switch unit varies current supplied to the left and right headlights from the battery according to control signals output from the controller.
In a preferred embodiment, the switch unit includes at least four transistors. The first transistor has a collector terminal connected to the battery, an emitter terminal connected to a first of two terminals of the left headlight, and a base terminal connected to the controller. The second transistor has a collector terminal connected to a second terminal of the left headlight, a grounded emitter terminal, and a base terminal connected to the controller. The third transistor has a collector terminal connected to the second terminal of the left headlight, an emitter terminal connected to a first of two terminals of the right headlight (a second terminal of the right headlight being grounded), and a base terminal connected to the controller. The fourth transistor has a collector terminal connected to the battery, an emitter terminal connected to the first terminal of the right headlight, and a base terminal connected to the controller.
When the ignition switch ON signal and the dimmer switch OFF signal are input to the controller, the controller performs control to operate the first transistor and the third transistor to ON, and the second transistor and the fourth transistor to OFF. When the ignition ON signal and the dimmer switch ON signal are input to the controller, the controller performs control to operate the first transistor, the second transistor, and the fourth transistor to ON, and the third transistor to OFF.